1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a device and method for controlling ink keys.
2. Background Information
U.S. Pat. No. 4,986,180 purports to disclose a device for controlling the opening of an ink fountain of a printing machine. A plurality of side-by-side lamellae or keys control how much ink is delivered to an ink roller by altering the distance between the lamella edge and the ink roller. Each key has a drive module, which has a control means, an amplifier, a drive unit, and an axle connected between the drive unit and the lamella. The control means may be a printed circuit board containing a processor and which receives signals from a bus line. The control unit accepts pulse signals, which the control means converts to control impulses for the amplifier. The amplifier converts the control impulses to into electrical power to switch on the drive unit which moves the axle to control the lamella. A detector is also provided to detect the location of the lamella and feed this location back to the control means.
All of the drive modules are connected through bus lines to a pre-amplification and interface unit. The bus lines have a plurality of extending parallel bus lines or wires and each of the control units is connected in parallel to every one of the wires. The pre-amplification and interface units are in turn connected to electronic data processing means which may be connected to a microcomputer or microprocessor in which an operator is able to communicate and operate by use of a keyboard and a screen.
U.S. Pat. No. 4,986,180 has the drawback that a separate bus line or wire is required for each drive module. The bus lines must often run through an electrically noisy environment and the large number of wires or lines in the bus can cause or be subject to electrical interference, resulting in malfunction of the control operations. Moreover, if a large number of keys are desired, the number of wires becomes large and the connections complication. In addition, the use of the pre-amplification and interface unit requires several connections, which are often the cause of malfunction or error. The described pulse control system also may not be highly accurate.
U.S. Pat. No. 5,052,298 describes an ink control system comprising a system CPU connected by serial lines to four servo power units, each power unit being connected to a plurality of server banks with servo modules, each servo module for adjusting one of the keys. Each servo power unit thus has a plurality of outputs for controlling different server banks. An operator console is connected to the system CPU via 24 discrete bus lines. The system described has several disadvantages including the large amount and type of wiring necessary.
An object of the present invention is to provide a reliable ink key control system. An alternate or additional object of the present invention is to provide an ink key control system with simplified wiring.
The present invention provides an ink key control system including a data processor, a local area network connected to the data processor and a plurality of ink keys connected directly to the local area network, each of the plurality of ink keys including a protocol controller for receiving an input from the local area network and a set point controller for receiving an input from the protocol controller.
Since each key of the present invention has a protocol controller and is directly connected to the local area network (LAN), a simplified and reliable key control system can be created. In particular, the amount of wiring can be reduced, and failure of a controller results in only a single key failure, rather than failure of a larger number of keys. The ink keys may further include an I/O driver for receiving an input from the setpoint controller, and a motor driven by the I/O driver. The motor can move to set a key blade for delivering a specific ink thickness from an ink fountain to an ink roller. The motor can be connected to a potentiometer which provides a feedback voltage depending on the position of the potentiometer, the feedback voltage being sent to an A/D converter. Alternatively a counter may be used to monitor the motor position. The A/D converter can output a digital value to the setpoint controller, which can then transmit this information in proper protocol form over the LAN. All of the electronics for a single key, including the protocol controller, setpoint controller, I/O driver and A/D converter, can be contained in a single key. The motor and pot, as well as the key blade, can be contained in the key as well.
Thus a plurality of discrete keys can be connected directly to the LAN, reducing wiring and improving reliability.
The LAN can be a commercial LAN such as PROFIBUS. The LAN communications protocol preferably incorporates a requested setpoint for a particular web, web side, color and key. The protocol controller determines when a message is for the protocol controller""s specific key and strips out the setpoint from the setpoint request. The setpoint is sent to the setpoint controller, which reads the setpoint request. The setpoint request is then compared to the actual setpoint, a direction of necessary movement is determined (if any), and the key is moved using the I/O driver to the setpoint using feedback from the motor through the potentiometer and the A/D converter.
A control algorithm of the setpoint controller ensures that the ink key motor is set within a certain set point window. The I/O driver switches the motor on and off. Changing the voltage polarity to the motor changes the motor direction. The potentiometer feedback is converted by the A/D converter to a digital value so that the setpoint controller can compare the actual position of the motor to the requested set point. Once the requested set point is within the setpoint window, the I/O driver can turn the motor off.
The key electronics may be driven by low power voltage, for example, 12 volts DC.
The present invention also provides a modular ink key comprising a housing and a LAN protocol controller, a setpoint controller, an I/O driver, and a motor inside the housing. The modular arrangement of the ink keys permits easy replacement as well as permitting simple connection to a LAN.
A method for setting ink keys is also provided comprising the steps of:
determining a setpoint for an ink key;
transmitting the setpoint over a LAN to the ink key,
receiving the setpoint at the key, and
setting the key as a function of the setpoint.
Preferably, the method also includes feeding back an actual position of the key to a setpoint controller. The setpoint is transmitted in a LAN protocol, which may be received by a protocol controller at the ink key.